A touch panel is an input device provided on a display panel such as a liquid crystal display panel and a plasma display panel to form a display device, and inputting information to the body of the display device by performing various types of operation on a screen of the display panel using a finger, a pen, etc.
Touch panels are classified into resistive-film, capacitive, infrared, ultrasonic wave, electromagnetic induction touch panels, etc., depending on their principles of operation. Of these, capacitive touch panels are relatively less likely to lose the optical characteristics of display devices, and are thus known as suitable for the display devices. In particular, projected capacitive touch panels are capable of multipoint detection of contact bodies such as fingers, and has thus excellent control characteristics of inputting complicated instructions.
In a touch region of a projected capacitive touch panel, which detects touch positions, a plurality of first electrode groups are arranged in parallel, each of which includes a plurality of first electrodes aligned in one direction, and a plurality of second electrode groups are arranged in parallel, each of which includes a plurality of second electrodes aligned in the direction orthogonal to the first electrode groups, as electrodes for touch position detection. The first electrodes and the second electrodes are made of transparent conductive oxide such as indium tin oxide (hereinafter referred to as ITO) having low conductivity to make the screen of the display panel see-through.
Each adjacent pair of the first electrodes of the first electrode groups is connected by a first connecting portion. Each adjacent pair of the second electrodes of the second electrode groups is connected by a second connecting portion. The first connecting portion and the second connecting portion are made of transparent conductive oxide, similar to the first electrodes and the second electrodes. In each of intersections between the first electrode groups and the second electrode groups, the first connecting portion and the second connecting portion are provided with an interlayer insulating film interposed therebetween to be insulated from each other. The first electrode groups and the second electrode groups are electrically connected to different lead lines drawn from the touch region to a terminal region located outside the touch region.
An external connecting terminal is provided at the top of each lead line. Each external connecting terminal is connected to a capacitance detection circuit, which applies AC voltages to the corresponding first and second electrode groups, and detects the capacitance at the portions corresponding to the first electrodes and the second electrodes. Each of the first electrodes, the second electrodes, and the lead lines are covered by a protective insulating film.
In this touch panel, when the insulating film is touched in the touch region, ones of the first electrodes and the second electrodes in the touch position are grounded via a capacitance generated between the electrodes and a contact body such as a finger, and via a human body. At this time, a change in the capacitance generated between the contact body and the ones of the first and second electrodes in the touch position is detected by the capacitance detection circuit. In this way, the touch position is detected based on the change in the capacitance.
In the terminal region of such a projected capacitive touch panel, numbers of external connecting terminals are densely arranged. The external connecting terminals need to be exposed from the insulating film to be connected to the external terminals, and thus are occasionally made of transparent conductive oxide such as ITO, which is resistant to moisture and heat, and less corroded, as well as electrodes for touch position detection as an anti-corrosion measure. (See, for example, PATENT DOCUMENT1.)